Abstract:
Two different heterogeneous catalysts, one with Cu(II) covalently bonded to functionalized mesoporous
silica (FMS-Cu(II)) and another with CuO nanoparticles immobilized over the same silica (FMS-CuO-np),
have been synthesized by a common route but with a minor alteration in the sequence of addition of
reagents. It is interesting to find that by merely changing the order of the addition of reagents Cu(II) can
be incorporated into the framework in two different forms. In one case Cu(II) binds to the N and O donor
centers present in the functionalized material whereas in the other case CuO nanoparticles are generated
in situ. The materials have been thoroughly characterized by powder X-ray diffraction, nitrogen adsorp tion/desorption, transmission electron microscopy, thermal analysis, FT-IR spectroscopy, solid state
MAS-NMR spectroscopy and atomic absorption spectrophotometric studies. The synthesized products
have been examined for their catalytic efficiencies in the oxidation of olefins, as a model case. Styrene,
α-methyl styrene, cyclohexene, trans-stilbene and cyclooctene have been used as substrates in the pres ence of tert-butyl hydroperoxide as the oxidant in acetonitrile medium under mild conditions. The pro ducts of the catalytic reactions have been identified and estimated by gas chromatography and gas
chromatography-mass spectrometry. The rate of conversion of the substrates for both the catalysts is
high and the selectivity is also good. But from comparative studies, it is found that FMS-CuO-np which
contains CuO nanoparticles shows better efficiency than FMS-Cu(II). The catalysts have been recycled for
five catalytic cycles without showing much decrease in their catalytic activity
